4,4′-Dichlorodiphenyl sulfone, abbreviated as DCDPS, is an organic sulfone with the formula (ClC6H4)2SO2. It is most commonly used as a key monomer in the manufacture of sulfone polymers.
Other dihalodiphenylsulfones than 4,4′-dichlorodiphenyl sulfone and related derivatives are also of great industrial importance. One can mention inter alia 4,4′-bis-(4-chlorophenylsulfonyl)biphenyl or 4,4″-bis-(4-chlorophenylsulfonyl)terphenyl.
DCDPS can be prepared by various ways. It is generally prepared by a two-step Friedel-Crafts sulfonation and sulfonylation reaction.
DCDPS can be synthesized as described by U.S. Pat. No. 4,983,773 by treating chlorobenzene with sulfuric acid at a temperature of 200-250° C. The reaction can be done in the presence of boric acid or trifluoromethanesulfonic acid, which increases the DCDPS yield by reducing the formation of the 2,4′ and 3,4′ isomers. The reaction goes to completion in approximately 10 hours and produces a high yield of 4,4′-dichlorodiphenyl sulfone.Cl-Ph+H2SO4→Cl-Ph-SO3H+H2OCl-Ph+Cl-Ph-SO3H→Cl-Ph-SO2-Ph-Cl+H2O.
The use of high temperature leads to a decrease in selectivity (80-87% of the 4,4′-isomer) and also requires the use of expensive corrosion resistant material of construction.
The use of lower temperatures has also been described. It gives a higher regioselectivity but requires activated substrates.
U.S. Pat. No. 3,415,887 describes the synthesis of DCDPS starting from sulfur trioxide, diethylsulfate and chlorobenzene. The reaction is exothermic and external cooling must be employed to maintain the temperature to a level not greater than about 15° C. in order to limit the decomposition of intermediate products. The reaction is carried out at lower temperatures and leads to a higher regioselectivity. Dimethylsulfate may also be used in replacement of diethylsulfate. However, the use of diethylsulfate or dimethyl sulfate has been firmly discouraged because of their great toxicity which causes significant issues associated with their use and transportation.
Tyobeka et al. describe in the Journal of the Chemical Society, Chemical Communications (1980), (3), 114-115, the use of a mixture of sulfuric acid and hexafluoroacetic anhydride as an efficient agent for the sulphonylation of aromatic compounds. In particular, they disclose the synthesis of DCDPS with 36% yield using monochlorobenzene, sulfuric acid and hexafluoroacetic anhydride in nitromethane. Nitromethane is carcinogen and explosive and its use is thus not recommended.
Thus, there remains an important need for an alternate route to manufacture dihalodiphenylsulfones and related derivatives with a high yield and high regioselectivity, at low temperature and in the absence of toxic or explosive reagents.